- waitpid PID,FLAGS
Waits for a particular child process to terminate and returns the pid of the deceased process, or
-1if there is no such child process. On some systems, a value of 0 indicates that there are processes still running. The status is returned in
$?. If you say
then you can do a non-blocking wait for all pending zombie processes. Non-blocking wait is available on machines supporting either the waitpid(2) or wait4(2) system calls. However, waiting for a particular pid with FLAGS of
0is implemented everywhere. (Perl emulates the system call by remembering the status values of processes that have exited but have not been harvested by the Perl script yet.)
Note that on some systems, a return value of
-1could mean that child processes are being automatically reaped. See perlipc for details, and for other examples.